Method and apparatus for replacing nozzles in erosion bits

ABSTRACT

Worn nozzles of an erosion bit are replaced without removing the drill string from the borehole by passing a holder provided with replacement nozzles through the drill string and orientably lodging the holder in the bit. The replacement nozzles are then transferred from the holder to the bit and thrust into abutting engagement with the bit nozzles. Each of the replacement nozzles is faced with viscoelastic material which upon deforming establishes a pressure seal between the contacting surfaces of the abutting nozzles.

United States Patent Maurer et al.

[ 1 Sept. 5, 1972 [54] METHOD AND APPARATUS FOR REPLACING NOZZLES IN EROSION BITS [72] Inventors: William C. Maurer, 7703 Primary Examiner Marvin A Champion g i' f i ig Assistant Examiner-Richard E. Favreau R f fi AttorneyJa.mes A. Reilly, John B. Davidson, Lewis ouston o H. Eatherton, James E. Gilchrist, Robert L. Graham Graham, 14326 Kellywood Lane, and James E Reed Houston, Tex. 77024 [22] Filed: March 1, 1971 [57] ABSTRACT v [21] Appl. N0.: 119,762 Worn nozzles of an erosion bit are replaced without removing the drill string from the borehole by passing a holder provided with replacement nozzles through [22] (SI ..l75/42E22,11;l5/l3}38 the drill String and Oriemably edging the holder in the d S 340 257 bit. The replacement nozzles are then transferred from 1 le c 6 the holder -to the bit and thrust into abutting engagement with-the bit nozzles. Each of the replacement nozzles is faced with viscoelastic material which upon [56] References Cited deforming establishes a pressure seal between the con- UNITED STATES PATENTS .tacting surfaces of the abutting nozzles.

2,169,223 8/ 1939 Christian 175/317 14 Claims, 8 Drawing Figures I 1 I 44 49- 50 52" 5O 49 I3 I l 23 v I I2 I I. I I

1 x. 3 I 33 l5 l4 METHOD AND APPARATUS FOR REPLACING NOZZLES IN EROSION BITS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to an improved method and apparatus for inserting replacement nozzles in an erosion bit.

2. Description of the Prior Art Erosion drilling, also referred to as high pressure drilling, is a technique for drilling boreholes using high velocity hydraulic jets as the principal mechanism for inducing stresses in formation rock. The basic components of an erosion drilling system include high pressure pumps, high pressure drill string, and an erosion bit provided with a plurality of flow nozzles. Erosion drilling systems normally employ water as the drill medium but other fluids including most drilling muds may also be used. The erosion bit can include auxiliary cutting devices such as cone cutters, drag bit blades, or a diamond crown. The principal drilling mechanism, however, is due to the erosional effects of high velocity jets impinging against the formation rock.

The power output of an erosion drilling system can be expressed as follows:

P= 0.0223 Apwhere P is the power output in horsepower;

p is the differential pressure in pounds per square inch; and

A is total nozzle flow area in square inches.

The differential pressure, p, is generally a fixed parameter controlled by the available pump pressure and pressure limitations of the surface and subsurface equipment. For a given pump pressure, then, and in accordance with the above equation, the power output, P, is directly proportional to the nozzle flow area A which is the combined flow area of all the bit nozzles.

Laboratory experiments have shown that the differential pressure, p, across the bit must be maintained at a threshold level in order to drill by the erosion mechanism. The threshold pressure for rocks normally encountered will vary between about 2,000 and 12,000 psi depending upon the cohesive strength of the rock. For example, the threshold pressure for hard rock such as limestone and marble falls between about 5,000 and 12,000 psi; whereas the threshold pressure for relatively soft sandstones is between about 2,000 and 4,000 psi. For all practical purposes, however, the threshold pressure must provide a jet velocity of at least 500 feet per second to attain reasonable rates of penetration. This jet velocity may be somewhat higher for hard rock drilling. At these high velocities, the jet streams tend to erode or wash out the nozzles in a relatively short period of time. Nozzle erosion is particularly severe where the drilling fluid contains even small amounts of abrasives such as silica sand. Nozzle erosion not only reduces the penetration rate but, if excessive, could increase the combined nozzle flow area to such an extent that the threshold pressure could no longer be attained. In this event, drilling by the erosion mechanism ceases. The bit then must be withdrawn from the borehole to replace the eroded nozzles even tough other bit components are in good repair. This involves withdrawing the entire drill string from the borehole, replacing the bit or nozzles, and rerunning the assembly into the borehole. This operation, known in the art as a round trip is time consuming and expensive, particularly for deep wells.

In order to prolong bit life and thus reduce the frequency of round trips, retrievable bits have been proposed. This type of bit generally includes a bit body secured to the lower end of a drill string and a retrievable nozzle holder mounted in the bit body. When assembled, these two members combine to form the bit. The nozzle holder can be separated from the bit body and retrieved by wireline equipment or similar devices. The retrievable bit is thus designed to permit replacement of nozzles by merely retrieving the nozzle holder and substituting a new one in its place. The obvious advantage of such bits is the savings in trip time since the drill string need not be withdrawn to replace bit components. Their main disadvantage is that the nozzle holder under the severe operating conditions of erosion drilling frequently cannot be dislodged from the bit body by wireline equipment. The tendency of the holder becoming stuck in the bit body is due primarily to the close fit required between the mating parts. When the assembly is subjected to high pressures, the holder is expanded or deformed resulting in an interference fit between the parts. Moreover, resilient sealing elements required to maintain a pressure tight assembly under high pressure tend to extrude between the mating parts. This material lodged between contact surfaces prevents relative movement of the parts. Also, silt or other detritus can collect at the assembly joints or between the mating parts. These factors, alone or in combination, result in a condition which makes the use of wireline equipment wholly impractical as the means for retrieving bit components. Reverse circulation techniques, e.g., pressuring the annulus to impose a dislodging force on the bottom surface of holder, are dangerous because of the strong likelihood of fracturing exposed formations.

Although the benefits of replacing nozzles without withdrawing the drill string from the borehole are well recognized, the prior art techniques are beset with difficulties which drastically limits their applicability in erosion drilling operations.

SUMMARY OF THE INVENTION The purpose of the present invention is to prolong the operable life span of the high pressure bit by inserting replacement nozzles in the bit when the original nozzles become eroded or when it is desired to alter the drilling characteristics of the bit. The invention resides in an improved erosion bit assembly and an improved method for replacing the nozzles in an erosion bit.

Briefly, the bit assembly comprises a bit adapted for connection to a tubular drill string and a pump-down nozzle holder. The bit can be provided with a central chamber and a plurality of flow channels extending through the lower wall of the body and exiting in a downward direction. The lower terminus of each channel contains a flow restriction which normally will be in the form of an insert nozzle. The size of the flow restriction determines the character of the jet exiting from the bit. The nozzle holder carries a plurality of replacement nozzles and is configurated to pass through the drill string and to enter the bit chamber in an oriented fashion. With the holder oriented in the bit chamber, each replacement nozzle is positioned in axial alignment with one of the flow channels formed in the bit. The replacement nozzles can then be transferred to the bit by hydraulic force and forced into abutting relation with the bit nozzles. Nozzle guide means are provided so that the abutting nozzles are disposed with their flow openings in axial alignment. Replacement nozzles are faced with packing material. This material under pressure deforms and establishes a pressure seal between the contacting surfaces. The replacement nozzles have flow openings smaller than those in the bit nozzles and, in effect, replace the worn or eroded bit nozzles when drilling operations are resumed.

The method includes the sequential steps of passing the nozzle holder through the drill string; orienting the holder in the bit; and transferring the replacement nozzles from the holder into the bit channels and into abutting engagement with the bit nozzles. The method thus achieves replacement of nozzles without withdrawing the drill string from the borehole and yet avoids many of the difficulties associated with prior art techniques.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal sectional view of an erosion bit and nozzle holder constructed according to the present invention.

FIG. 2 is a-bottom plan view of the bit shown in FIG. 1.

FIG. 3 is a view similar to FIG. 1 illustrating the nozzle holder orientably lodged in the erosion bi t.

FIG. 4 is 'a transverse sectional view of the bit and nozzle holder shown in FIG. 2, the cutting plane taken generally along the plane indicated by line 4-4.

FIG. 5 is an enlarged exploded view of a replacement nozzle assembly capable of use in the present invention.

FIG. '6 is an enlarged fragmentary view of the bit shown in FIG. 2, illustrating the manner in which a replacement nozzle seats in a bit nozzle.

FIG. 7 is an elevational view with portions cut away of a bit assembly, illustrating the present invention in connection with a tri-co'ne bit.

FIG. 8 is a bottom plan view of the bit shown in FIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described first in connection with a high pressure drag bit (FIGS. 1-6) and then, briefly, in connection with high pressure cone bit (FIGS. 7 and 8). It should be realized that it is not essential that the bit be equipped with the particular type of auxiliary cutting devices disclosed. It is essential, however, that the bit be constructed in such a manner to develop high velocity jets. This is normally achieved by attaching to the bit a plurality of flow nozzles sized to develop high velocity jets under a pressure differential attainable by available pumping facilities. The number, size, and arrangement of the nozzles on the bit will depend upon several factors including the type of rock to be drilled, hydraulic capacity of pumping facilities, size and type of the bit. Drag bits and diamond bits present no serious space problems and therefore can accommodate several nozzles arranged in a variety of patterns. From about three to about 12 nozzles are normally arranged on the bottom surface of these bits to provide a widely distributed jet pattern. For cone bits, the number of nozzles which can be accommodated is limited by available space for mounting the nozzles. Tri-cone bits, for example, normally can accommodate only three nozzles.

The size of erosion bits normally will range between about 4% inches and 9 7/8 inches and will be designed to operate at differential pressures between about 2,000 and 15,000 psi. Nozzle openings can be any size capable of developing high velocity jets but usually are between one-eighth and one-fourth inches.

With reference to FIGS. 1-6, a drag bit 10 constructed of forged steel is shown connected to the lower end of a tubular drill string 11. The bit 10 includes an upper section 12 provided with a threaded shank 13 and a lower section 14 provided with three radial wings 15, 16, and 17. Mounted on the lower edge of each wing is a cutting blade. The blades, illustrated as 18, 19, and 20, can be welded to the bit 10 and can be faced with wear resistant materials such as tungsten carbide. Alternatively, the cutting blades can be integrally formed in the bit body and surfaced with wear resistant material. The outer peripheries of the blades and wings can be surfaced with diamonds to maintain bit gauge. The leading edges of each blade extend in a radial direction from the longitudinal axis of the bit 10 and are disposed to effect a cutting action attendant to counterclockwise rotation of the bit 10 as viewed in FIG. 2. A central, circular chamber 21 extends axially through the upper section 12 of the bit 10 terminating in abottom wall 22. The chamber 21 has an upper, full opening section 23 and a lower section 24 of reduced cross diameter. The diameter of section 23 can be about equal to the internal diameter of the drill string 11, and the diameter of section 24 can be about oneeighth inch less than the diameter of section 23.

Referring to FIG. 2, each of the wings are provided with a set of nozzles, wing 15 carrying nozzles 25 and 26, wing 16 carrying nozzles 27 and 28, and wing 17 carrying nozzles 29 and 30. A central nozzle 31 is located near the longitudinal axis of the bit 10. Circular flow courses interconnect the nozzles and the central chamber 21. As illustrated in FIG. 1, flow courses 32, 33, and 34 lead from the central chamber 21 to nozzles 25, 26, and 31, respectively. Nozzles 27-30 are similarly provided with flow courses.

All flow courses except flow course 34 extend laterally from the chamber 21 and curve gently downwardly exiting through the bottom surface of the bit 10 in a linear direction. The diameter of each flow course is maximum at the inletand diminishes gradually to a minimum in the lower linearly extending section. The central flow course 34 extends axially through bottom wall 22 and curves radially outwardly and, like the other flow channels, is tapered. The discharge ends of each flow course can be threaded for receiving a nozzle, as illustrated in the drawing. The outermost nozzles 25, 27, and 29 can be tilted radially outwardly and the central nozzle 31 can be tilted away from the axis of the bit. The diameter of each flow course and the degree of curve in each should be such to permit easy passage of a replacement nozzle as described in detail below.

The bit can be constructed by first forging separate longitudinal segments denoted 35, 36, and 37 in FIG. 2, welding the segments together, and finally machining the assembled bit to provide the threaded shank 13, the threaded flow courses, and the proper dimensions in chamber 21. The forging and machining can be performedby techniques well known in the bit making art.

Nozzles which can be connected to the bit 10 are shown in detail in FIG. 6. In order to be distinguished from the replacement nozzles described later, these nozzles will be referred to as bit nozzles. Each bit nozzle includes a threaded steel sleeve 38 and a hollow insert member 39. The sleeve 38 can be provided with a hex head 40 to facilitate mounting the nozzle on the bit. An o-ring mounted in a suitable groove in sleeve 38 provides a fluid tight joint across the threaded connection. The insert member 39 normally will be made of wear resistant material such as tungsten carbide. Tungsten carbide objects can be secured in the sleeve 38 by known brazing techniques. The opening through the nozzle assembly is in the form of a straight circular section 42 and a tapered inlet 43. The degree of the taper of inlet 43, preferably, should be gradual, defining an included angle between about and about 35 degrees and should constitute at least 30 percent of the axial dimension of the bit nozzle measured along its longitudinal axis. The transition from the steel sleeve 38 to the insert member 39 through the tapered section 43 is smooth. The tapered inlet configuration can be formed by techniques known in the art.

As shown in FIG. 1, the bit nozzles extend beyond the lower surface of the bit 10 but not beyond the lower extremity of the blades 18-20. This permits locating the nozzles at the desired standoff distance from the formation.

During drilling operation, fluid flow will be through the drill string 11, through the bit flow courses, e.g., 32, 33, 34, and finally through the bit nozzles 25-31. The jets discharging from the nozzles impinge against the formation and cut circular kerfs therein as the bit is rotated. The islands of formation rock separating the kerfs are abraded by the cutting blades 18-20. Experience has shown that at the high jet velocities, the bit nozzles 25-31 become eroded in a relatively short period of time. In flow tests using sintered tungsten carbide nozzles, the flow area of 0.1 inch was increased by about 28 percent after only 3.2 hours of fluid flow. The tests consisted of flowing water containing 2 volume percent of sand through the nozzles at a pressure differential of between 10,000 and 14,000 psi.

The present invention increases the life span of the bit by functionally replacing the bit nozzles with new nozzles. The replacement nozzles are carried from the surface to the bit 10 in a specially configurated nozzle holder. The nozzle holder is orientably lodged in the bit to align each replacement nozzle with oneof the bit flow courses. The replacement nozzles are then transferred from the holder to the bit and forced into abutting engagement with the bit nozzles. The replacement nozzles are faced with packing material which deforms under stress and establishes a pressure seal in the area of contact between the nozzles. The openings of the replacement nozzles are smaller than the openings of the bit nozzles and thus define the minimum flow restriction in the system. In effect, then, the replacement nozzles replace the bit nozzles.

As shown in FIGS. 1 and 3, a nozzle holder 44 suitable for use in the present invention can be in the form of a cylindrical plug having a plurality of circular channels formed therein. A replacement nozzle is mounted in each channel; thus, if it is desired to replace all the bit nozzles 25-31, the holder 44 will be provided with one channel for each bit nozzle. As shown in FIG. 1, replacement nozzles 51 and 52 carried in channels 45 and 46 are adapted to align with the flow courses 32 and 33 formed in wing 15. Each channel is placed in axial alignment with a flow course when holder 44 occupies predetermined angular position in chamber 21. Although not shown in the drawing, channels containing replacement nozzles for nozzles 27-30 are similarly placed in alignment with their flow courses formed in wings 16 and 17. It should be observed that the paired channels,'e.g., 45 and 46, containing replacement nozzles 51 and 52 can be aligned with the flow channels of either of the other wing flow courses depending upon the angular position of the holder 44. For example channels 45 and 46 align with the flow courses of either wing 16 or 17 when the holder 44 is turned in either direction from the position shown in FIG. 2. Thus, the three paired sets of channels in holder 44 can align with either the flow courses of wing 15, the flow courses of wing 16 or the flow courses of wing 17. Central channel 47 extends axially through the, holder 44 and carries replacement nozzle 53. Channel 47, and hence nozzle 53, align with central flow course 34 in any angular position of the holder 44 in chamber 21.

The nozzle holder 44 is sized to pass through the drill string 11 and to enter the bit chamber 21. An annular seal 48 which can be in the form of an O-ring extending around the outer periphery of the holder 44, is adapted to engage interior of section 24 with the holder 44 lodged in chamber 21. The provisions of the annular seal 44 permits the holder to mate in the lower section 22 in a relatively loose fit, clearances of between 0.010 and 0.015 inches being satisfactory for most applications. Except for central channel 47, all of the channels can be bored through the top surface of the holder 44 exiting through the outer periphery thereof. An upper section of each channel can be counterbored for receiving a cup-like member identified by reference 49 in the drawings. The cup-like member 49 is designed to fit snugly in the counterbored section of each channel. A small hole 50 formed in the base of the member 49 permits the transmission of fluid through the channel. The cup-like member 49 can be made of copper, aluminum, or other easily erodible material. Each replacement nozzle can be inserted in a cup-like member 49 and the resulting assembly then inserted through the top of the nozzle holder 44 into a channel. Each assembly is pressed downwardly into its corresponding channel until the rim of member 49 abuts the shoulder of the counterbore. The replacement nozzles are frictionally held in this position as the holder 44 is pumped through the drill string 1 l.

The means for orienting the nozzle holder 44 in the bit can take a variety of forms. In the present embodiment a pin and groove arrangement is employed. A pin 54 extends upwardly from the bottom wall 22 of chamber 21 and is disposed between the axis and the outer wall of chamber 21. The bottom surface of the holder 44 is provided with three conical recesses, shown in FIG. 4 as 55, 56, and 57. The apex of each recess is disposed to register with the tip of pin 54 with the holder 44 lodged in the lower section 24 of chamber 21. The bases of recesses 55, 56, and 57 intersect in lines 58, 59, and 60. Thus, as the holder 44 approaches bottom wall 22 of chamber 21, pin 54 engages a flank of one of the recesses 55, 56, or 57. Further downward movement of the holder 44 causes it to be turned until the tip of pin 54 is lodged in the apex of one of the recesses 55-57. This places each of the paired channels of holder 44 in alignment with one of the paired flow courses of the bit. In this embodiment, the maximum turning required to orient the holder is about 60. F

The replacement nozzles are specially constructed to fit snugly in the cup-like member 49 and to be frictionally held therein. As-shown in FIG. 5, the replacement nozzle comprises a hollow ceramic member 61, e.g., tungsten carbide, having a cylindrical section 62 and a tapered nose section 63. The diameter of section 62 should be slightly less than the minimum diameter of the bit flow courses. The taper of the nose section 63 is slightly less than the taper of the inlet 43 of the bit nozzle (see FIG. 6). The included angle defined by the tapered nose section 63 can be from l to less than that defined by the tapered inlet 43 of the bit nozzle. An opening 64 extends axially through the ceramic member 56 and can be provided with a tapered inlet as illustrated. The nose section 63 is faced witha packing material capable of deforming under stress to establish a pressure seal when contacting another surface. The

packing material normally will be a viscoelastic plastic and can be provided by a separate member 65 shaped to clip on the nose section 63 or can be molded directly on the ceramic member 61. Suitable viscoelastic materials include polymers or copolymers of one of the fluoroplastics, nylon or hard rubber. Polytetrafluoroethylene is preferred because of its low coefficient of friction and its anti stick characteristic enhance plastic flow adjacent a metal surface. An epoxy resin or other suitable adhesive can be used to secure the molded member 65 to the ceramic member 61 if desired.

Anannular groove 66 formed of an intermediate portion of the nose 63 is adapted to receive a complimentary shaped protrusion 67 formed on the interior of the memberv 65. This adds physical bonding strength to the assembly. The thickness of the packing member 65 should be uniform throughout the lower portion of the nose member. The thickness can vary but normally will be between about one-sixteenth and about one-fourth inches. The outer extremity member 65 should be flush with the outer periphery of the cylindrical section 62.

A plug 68 composed of a deformable material such as nylon, rubber, or polytetrafluoroethylene is inserted through the opening 64 of the replacement nozzle. The plug 68 has an enlarged head 69 which seats at the base of the tapered inlet of opening 64. When inserted in the replacement nozzle, the plug 68 extends beyond the nose section 63 and serves as a guide to bring the openings of the replacement nozzle and the bit nozzle into axial alignment. Theparts shown in FIG. 5 can be preassembled and inserted in a holder channel, one of such assemblies for each channel. The plug 68 closes opening 64 and thus permits the development of hydraulic force for transferring the replacement nozzles from the holder 44 to the bit 10 as described below.

In operation, an erosion bit 10 similar to the one depicted in FIGS. 1 and 2 will be run in the drill string 11 and operated until the bit nozzles become sufficiently worn to require replacement. This condition will generally be indicated by reduced drilling rate or reduced drilling pressure. At this time, the nozzle holder 44 provided with the replacement nozzles will be passed through the drill string 11 and into the bit chamber 21. This can be achieved by inserting the holder 44 into the drill string and pumping drilling fluid behind the holder 44 forcing it downwardly toward the bit 10 (see FIG. 1). Alternatively, the holder 44 can be placed by use of wireline equipment. In either event, the holder 44 enters the lower section 24 of chamber 21 and is oriented therein by means of the pin 54 engaging one of the conical recesses 55-57 (see FIG. 2). With the holder 44 oriented, O-ring 48 prevents passage of fluid around the holder 44 so that an increase in pressure in the drill string 11 is transmitted through the cup-like member 49 via hole 50 forcing the replacement nozzle assemblies from the holder 44. The sealing ability of O-ring 48 need not be large since it must withstand only that pressure required to dislodge the replacement nozzles from the holder 44. Each nozzle thus passes into an aligned flow course and is forced downwardly into abutting engagement with a bit nozzle. The holes 50 in the cup-like members 49 temporarily maintain a small differential pressure between fluid in the drill string 11 and fluid in the flow channels. This insures that all of the replacement nozzles will be discharged from the holder 44. As each replacement nozzle approaches the' lower end of its flow course, the tip of the plug 68 enters the opening of the bit nozzle. The replacement nozzle is thus properly lodged in a bit nozzle, the openings of each being in axial alignment. As the pressure upstream of the nozzles is increased, the replacement nozzle is forced downwardly into abutting engagement with its associated bit nozzle causing the packing material to deform. At a predetermined pressure, the head 69 of the plug 68 will yield allowing the plug 68 to clear the replacement nozzle and to pass through the bit nozzle.

Plastic flow in the zone to be sealed will be between the points of maximum stress. The difference in the taper of nose 63 and the taper of inlet 43 creates a highstress boundary in the area indicated by reference numeral 70 (FIG. 6). The upper boundary is defined by the upper extremity of the nose section 63 positioned in close conformity to the wall defining the bit flow. This boundary is indicated by reference numeral 71 (FIG. 6). Thus plastic flow will be upwardly from boundary 70 section and downwardly from boundary 71. This plastic flow causes the viscoelastic material to fill the irregular annular space between the nose section 63 and the outer wall defined by the tapered inlet 43 and the flow course wall. The packing pressure in this zone will generally be higher than the pressure upstream of the replacement nozzle. The high pressure zone establishes an effective pressure seal. With the replacement nozzles sealingly seated in the bit nozzles, the small flow restriction provided by the former determines the character of the jet emerging from the bit 10. In effect, then, the replacement nozzles replace the bit nozzles when drilling is resumed. Under normal drilling conditions members 49 are rapidly eroded away removing the flow restrictions in each of the channels. This condition is illustrated in FIG. 2.

As mentioned previously, the present invention can be used in conjunction with cone bits as well as drag bits. A cone bit 72 is shown in FIGS. 7 and 8 as having a body 73 provided with a threaded shank 74, and three cones 75, 76, and 77 journaled to the body 73. A circular chamber 78 extends through the shank 74 and into the body 73 terminating at end wall 79. The chamber 78 has a full opening section 80 and a section of reduced diameter 81. The bit 72 is also provided with three nozzles 82, 83, and 84. The nozzles are disposed between the bases of the cone cutters 75-77 and are directed in a generally downwardly direction. Flow courses, one shown as 85 in FIG. 7, extend from the chamber 78 exiting through the bottom surface of the bit body 73. The lower end of the flow course 85 is counterbored for receiving an extension tube 86. The extension tube 86 fits into the counterbored section and is welded to the body 73 as illustrated. The lower end of the tube 86 is threadedfor receiving a bit nozzle, e.g., nozzle 82. The interior of the tube 86 is sized to provide a smooth continuation of flow course 85. ..T he fiow course thus extends in a linear direction away from chamber 78, curves downwardly through tube 86 and exits in a linear direction. The flow passage through the body 73 and tube 86 can be tapered to minimum diameter in the lower linear section. The tapered configuration serves to guide the replacement nozzles into the bit nozzles. Nozzles 83 and 84 are similarly connected to the bit body 73 by extension of tubes 87 and 88, respectively, as shown in FIG. 8.

A nozzle holder 89 in this embodiment can be similar to the nozzle holder described previously. The holder 89 has formed therein three channels, one shown as 90, and each channel is provided with a cup-like member 91 having a hole 92 formed in its base. Each channel receives a replacement nozzle 93 which can be of the same general construction previously described and illustrated in FIG. 5. Lip seals 94 mounted about the outer periphery of the holder 89 provide a pressure seal around the upper portion of the holder lodged in the chamber 78. The means for orienting the nozzle holder 89 in the bit chamber 78 can be the pin and groove arrangement described previously. Pin 95 extending upwardly from the bottom wall 79 is adapted to engage one of three conical recesses, one shown as 96. With the holder oriented in the chamber 78, each channel, e.g., 90, is aligned with the flow course, e.g., 85, in the bit body 73. The replacement nozzles, e.g., 93, can be pressure discharged from the nozzle holder 89 and forced into abutting engagement with a bit nozzle, e.g., 82, as illustrated in FIG. 7. When drilling operations resume, the drilling fluid flowing through the holder quickly erodes away the base of the cup-like member 91.

Advantages of the present bit assembly over prior bits, particularly retrievable bits, used in erosion drilling operations, are that the nozzle holder need not be machined within close tolerances to provide a pressure seal, and the holder need not be retrieved from the bit to effect replacement of the bit nozzles.

We claim:

1. An assembly comprising a bit adapted for connection to a tubular drill string, said bit having a plurality of How courses extending therethrough, each of said flow courses terminating in a flow restriction of reduced cross section; a holder passable through said drill string and into said bit and containing a plurality of replacement nozzles detachably mounted therein, a leading portion of each said replacement nozzles being faced with packing material; means for orienting said holder in said bit body to align each of said nozzles with one of said flow courses; and means for discharging each of said replacement nozzles from said holder into an aligned flow course and into abutting engagement with one of said flow restrictions.

2. An assembly as defined in claim 1 wherein said packing material is polytetrafluoroethylene.

3. An assembly as defined in claim 1 wherein the means for orienting said nozzle holder in said bit includes a member mounted in said bit and a cooperating surface found on said nozzle holder, said surface adapted to engage said member as said holder enters said bit and to guide said holder to said oriented position.

4. An assembly as defined in claim 1 wherein each of said replacement nozzles is provided with a plug for sealing the opening thereof, said plug being removable from said replacement nozzle at a predetermined pressure differential across said replacement nozzle.

5. An assembly as defined in claim 4 wherein said plug mounted in said replacement nozzle extends beyond the leading portion of said replacement nozzle and is sized to enter one of said flow restriction of said bit.

6. An assembly as defined in claim 1 wherein the means for discharging said replacement nozzles from said nozzle holder includes hydraulical means operative to force said replacement nozzles from said holder and into said bit flow courses.

7. An assembly as defined in claim 6 wherein said nozzle holder further includes a sealing element mounted about its outer periphery, said sealing element being sized to engage an interior surface of said bit with said holder lodged therein to establish a pressure seal between said nozzle holder and said bit.

8. An assembly as defined in claim 7 wherein said nozzle holder further includes a means for establishing a temporary flow restriction above each replacement nozzle carried therein.

9. An assembly as defined in claim 1 and further comprising a plurality of cutter cones journaled to said bit.

10. An assembly as defined in claim 1 and further comprising a plurality of cutter blades mounted on said bit.

11. A replacement nozzle for inserting into an erosion bit, and adapted to sealingly engage a bit nozzle, said replacement nozzle comprising a hollow ceramic member; and a viscoelastic member mounted on a leading portion of said ceramic member, said viscoelastic member being deformable under stress to establish a pressure seal in the area of contact between the replacement nozzle and bit nozzle.

12. A replacement nozzle as recited in claim 11 wherein said viscoelastic member is composed of polytetrafluoroethylene.

13. A method for inserting a nozzle into an erosion bit attached to a drill string and having at least one flow course extending therethrough, said flow course terminating in a bit nozzle, said method comprising passing a holder through the drill string and into said bit, said holder having a replacement nozzle detachably mounted therein, the leading portion of which is composed of packing material; orienting said holder in said bit to align said nozzle with said flow course; transferring said nozzle from said holder to said flow course; increasing the pressure in said drill string and said bit to UNITED STATES PATENT OFFICE CERTIFICATE OF (,ZQERECTION Patent No. 3,688,853 Dated September 5, 1972 Inventor(s) William C. Maurer, et a1 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the bibliographic data, insert:

[73] Assignee: Esso Production Research Company At Column 4, line 37, delete "cross";

At Column 6, line 23, change "2" to 3-v-; At Column 6, line 25, delete "either";

At Column 6, line 38, change "22" to 24-; At Column 8, line 18, change "2" to 3-;

i At Column 8, line 53, after "flow" insert -'course-;

At Column 9, line 4, change "2" to 3--;

At Column 10, line 5, before "holder" insert -nozzle;

At Column 10, line 22, change third occurrence of "said" to -an At Column 11, line 9, before "nozzle" insert -replacement-; At Column 11, line 10, before "nozzle" insert --replacement;

At Column 12, line 1, before "nozzle" insert --replacement-;

At Column 12, line 8, change second occurrence of "said" to an Signed. and sealed this 13th da of March 1-973.

SEAL} Attest:

EDWARD M. FLETCHER,JR. ROBERT QOTTSCHALK Attesting Officer Commissioner of Patents FORM PO-IOSO (10-69) USCOMM DC 6o376 p69 n u s GOVERNMENY Pmm'mc orrlcz I969 0- 366-33A 

1. An assembly comprising a bit adapted for connection to a tubular drill string, said bit having a plurality of flow courses extending therethrough, each of said flow courses terminating in a flow restriction of reduced cross section; a holder passable through said drill string and into said bit and containing a plurality of replacement nozzles detachably mounted therein, a leading portion of each said replacement nozzles being faced with packing material; means for orienting said holder in said bit body to align each of said nozzles with one of said flow courses; and means for discharging each of said replacement nozzles from said holder into an aligned flow course and into abutting engagement with one of said flow restrictions.
 2. An assembly as defined in claim 1 wherein said packing material is polytetrafluoroethylene.
 3. An assembly as defined in claim 1 wherein the means for orienting said nozzle holder in said bit includes a member mounted in said bit and a cooperating surface found on said nozzle holder, said surface adapted to engage said member as said holder enters said bit and to guide said holder to said oriented position.
 4. An assembly as defined in claim 1 wherein each of said replacement nozzles is provided with a plug for sealing the opening thereof, said plug being removable from said replacement nozzle at a predetermined pressure differential across said replacement nozzle.
 5. An assembly as defined in claim 4 wherein said plug mounted in said replacement nozzle extends beyond the leading portion of said replacement nozzle and is sized to enter one of said flow restriction of said bit.
 6. An assembly as defined in claim 1 wherein the means for discharging said replacement nozzles from said nozzle holder includes hydraulical means operative to force said replacement nozzles from said holder and into said bit flow courses.
 7. An assembly as defined in claim 6 wherein said nozzle holder further includes a sealing element mounted about its outer periphery, said sealing element being sized to engage an interior surface of said bit with said holder lodged therein to establish a pressure seal between said nozzle holder and said bit.
 8. An assembly as defined in claim 7 wherein said nozzle holder further includes a means for establishing a temporary flow restriction above each replacement nozzle carried therein.
 9. An assembly as defined in claim 1 and further comprising a plurality of cutter cones journaled to said bit.
 10. An assembly as defined in claim 1 and further comprising a plurality of cutter blades mounted on said bit.
 11. A replacement nozzle for inserting into an erosion bit, and adapted to sealingly engage a bit nozzle, said replacement nozzle comprising a hollow ceramic member; and a viscoelastic member mounted on a leading portion of said ceramic member, said viscoelastic member being deformable under stress to establish a pressure seal in the area of contact between the replacement nozzle and bit nozzle.
 12. A replacement nozzle as recited in claim 11 wherein said viscoelastic member is composed of polytetrafluoroethylene.
 13. A method for inserting a nozzle into an erosion bit attached to a drill string and having at least one flow course extending therethrough, said flow course terminating in a bit nozzle, said method comprising passing a holder through the drill string and into said bit, said holder having a replacement nozzle detachably mounted therein, the leading portion of which is composed of packing material; orienting said holder in said bit to align said nozzle with said flow course; transferring said nozzle from said holder to said flow course; increasing the pressure in said drill string and said bit to force said nozzle into abutting engagement with said bit nozzle and to deform said packing material and thereby effect a pressure seal in the contact area between said replacement nozzle and said bit nozzle.
 14. A method as defined in claim 13 wherein the step of transferring said replacement nozzle includes increasing the pressure in said drill string to forcE said replacement nozzle from said holder and into said aligned flow course. 